JP2000243272A - Manufacture of x-ray image intensifying tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an X-ray image intensifying tube, capable of realizing a relatively high crack frequency in a luminescent material layer. SOLUTION: A feature of this manufacturing method of an X-ray image intensifying tube provided with an entrance screen having a support member 34 for arranging a luminescent material layer and a photocathode is that the luminescent material layer is deposited by vapor-depositing it at an inclination of θ deg. with respect to a center line 32 perpendicular to the screen, and the temperature of the support member is raised from room temperature to the maximum temperature during the deposition of the luminescent material layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an X-ray image intensifier having an entrance screen having a support member on which a light emitting material layer and a photocathode are provided.

[0002]

Such a method is known from US Pat. No. 3,821,633. It describes an X-ray image intensifier tube having a luminescent material layer made of CsI, in which a structure is formed in the luminescent material layer. On the other hand,
Structures are formed in the layer of CsI described in this patent, due to the deposition parameters applied for this purpose, such as substrate temperature, deposition rate, and the like. On the other hand, as described in this patent, additional structures can be formed by heat treatment of the luminescent material layer.
The layer having such a structure is cracked (cracked).
ckled)) is known as a layer having a structure. An X-ray image intensifier provided with a light-emitting material layer having such a structure has been proved to perform satisfactorily, but in particular, the demand for the resolution of the X-ray image intensifier has been significantly increased. It has become necessary to optimize the structure for this purpose. In practice, this means that a higher crack frequency is achieved in the luminescent material layer.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing an X-ray image intensifier tube which satisfies these requirements, and in order to achieve this object, a method described in the opening paragraph. However, the light emitting material layer is deposited by vapor deposition obliquely to a center line perpendicular to the screen.

Due to the fact that the luminescent material is deposited obliquely to a center line perpendicular to the support member, it extends over the layer and has a cross section of, for example, several μm to tens of μm, ie, for example, 10,000 lines / cm for 1 μm and for example 5
Crack between 200 lines / cm for 0μm
The structure of a very fine column of CsI with frequency is obtained. The above structure of the luminescent material layer can be adapted to the desired resolution by constructing a column with an average cross-section that represents a realistic fraction of the image pixel size on the screen. A practical fraction is between about 5 and 20 column diameters per pixel diameter to image with acceptable edge resolution. The spacing between columns is preferably greater than or equal to about 0.25 μm, since the smaller the value, the worse the optical separation. Further, the interval between columns is preferably about 2 μm or less, because the blocking ability of the light emitting material layer is reduced when the value is more than about 2 μm.

In a preferred embodiment, the angle of incidence, which is the angle between the direction in which the luminescent material is to be deposited and the center line perpendicular to the screen, is greater than about 30 °. The luminescent material layer is
For example, it is preferably obtained by vapor deposition from a crucible to be heated filled with a luminescent material. The uniformity of the deposited luminescent material layer is promoted by rotating the deposition crucible and the support member with respect to each other, preferably such that the deposition crucible circles on a conical surface with respect to the center of the support member. In that case, it is preferable that the light emitting material layer be rotated several times in vapor deposition.

The X-ray image intensifier manufactured according to the present invention is characterized in that the luminescent material layer has a column structure, and the columns of this column structure have an average transverse dimension of at most about 25 μm, and the columns have a width of 0.5 μm to Separated by cavities having a width in the range between 3 μm, at most a few columns are characterized by having rather large transverse dimensions. It should be noted that the voids between the columns (hereinafter simply referred to as gaps) in this case do not clearly imply the type of gap corresponding to the cracks according to the prior art. The gap is often formed by a series of bubbles in the form of a generally elongated bubble, and advantageously, the longitudinal direction of said generally elongated bubble extends in the direction of the series of bubbles. Between bubbles, the columns can come into contact with each other, but this results in relatively little optical contact. When measured in the longitudinal direction, the bubble is approximately 90% of the serial length.
%, While nodes between bubbles also do not make good optical contacts unless otherwise taken, and the situation is rather the opposite. The oblique deposition according to the invention has a good effect on bubble formation. The gap thus obtained shows more or less an intermediate morphology between the cracks and the separation between the deposited ore pillars, which are, for example, in principle individual crystals.

[0007] A well adapted screen structure for high resolution can be achieved, for example, with a substrate temperature of about 20 ° C starting at about 20 ° C, realized by a well chosen deposition rate and heat transfer from the screen. Can be realized by the vapor deposition according to the present invention, which reaches a maximum temperature not exceeding.

An embodiment of the present invention will be described with reference to the drawings.

[0009]

FIG. 1 shows an entrance screen 8 of an X-ray image intensifier tube 1 according to the invention, housed in an envelope having an entrance window 2, an exit window 4 and a sheath 6, and an exit. screen
10 and an electron optical system 12 having a first electrode 14, a second electrode 16, and a final electrode 16 are shown. Entrance screen 8
Are arranged as separate screens in the image intensifier in this example, but may be provided directly on the entrance window. The entrance screen 8 comprises a support or substrate 20, for example made of aluminum foil, having a thickness of, for example, 0.5 μm, on which a light-emitting layer 22 made of CsI (Na) or CsI (Ti) is provided. A photocathode 21 is provided thereon with a separation layer (not shown) interposed as necessary. The X-ray image 25 incident on the entrance window is converted into a light / optical image in the light emitting layer, and as a result, a photoelectron image 26 is generated in the photocathode. The photoelectron image 26 is imaged on the exit screen by the electron optics 12 that significantly accelerates the photoelectrons,
It is converted into a light / optical image 28. The light / optical image 28 can be observed from outside the image intensifier tube.

[0010] For satisfactory operation and to reduce patient dose, it is desirable that the emissive layer have a relatively high X-ray absorption. X-rays that are not captured by the luminescent screen do not contribute to imaging and form a radiation load on the patient. Thus, the luminescent screen will need to be relatively thick, for example, 200-400 μm. For example, 3
A thickness of 00 μm reliably captures 75% of the X-ray radiation.
In a "normal" deposited layer of CsI which is considerably more transparent, the emitted light will diffuse significantly from the emission center, especially on the incident side of the layer. This situation is remedied by choosing the deposition conditions such that a structured layer is obtained. Therefore, in particular, the substrate temperature, especially the temperature of the support member at the beginning of the deposition, is important. A photograph (preferably imaged by a scanning electron microscope) of a cross section of the layer shows that the structure is formed by columnar crystals, the longitudinal direction of which is substantially coincident with the thickness direction of the layer. Due to this structure, the diffusion of the emitted light is reduced, but to a lesser extent. This is because the optical separation at the transition between the various columns is insufficient. This is due to the fact that the width of the interruption is insufficient and on average is much smaller than the wavelength of the emitted light (roughly 0.5 μm). Significant improvements are achieved when a cracked structure is provided in the layer as described in US Pat. For example, a column is formed by combining a large number of columns by an adaptive thermal method. This column does not have a clear optical separation wall inside, but there is a clear optical separation wall between the columns. The fineness of the crack structure can be significantly influenced by the nature of the heat treatment, and in some cases by structuring at the surface of the support member. Various methods are known for this purpose.

In the production of the entrance screen for the X-ray image intensifier according to the invention, the starting material may be a support member which is intentionally unstructured. FIG. 2 shows very diagrammatically an apparatus for carrying out the deposition method according to the invention. In the space 30 to be evacuated, a support member or substrate 34
And a deposition crucible containing a luminescent material and comprising a heating element 38
36 are arranged rotatably about the shaft 32 in this example. The support member 34 can be rotated around the shaft 32 via the insertion member 40. Alternatively, the crucible 36 can be rotated about the shaft 32 via the bracket 44 and the insertion member 46. The axis 32 preferably coincides with a center line perpendicular to the support member, which in this example is a spherical segment that is a partial spherical surface with a center 50. For vertical deposition at least at the center point 0 of such a support member, the deposition crucible is located on line 32, but for vertical deposition over the entire screen, the deposition crucible is located at point 50. It must be.

In the vapor deposition process according to the present invention, a vapor deposition crucible is disposed on the side of the shaft 32. The illustrated crucible 36
, A deposition angle θ ° is obtained. The symbol θ ° is used to indicate that this angle matches the center point 0 of the screen. It will be apparent from the figure that the angle of incidence varies with position on the support member. In the rotation, the deposition is performed while changing the angle over the entire support member. However, to state correctly, the center point 0
Except for the two deposition angles are related, ie, the slope, the angle to the local main line that is constant in rotation about the center point 0, and the azimuth that changes about the center point 0 during rotation over 360 °. Consider that corners are related.

When the entire light emitting layer is vapor-deposited, it is preferable that the support member is rotated many times, for example, several tens to several thousands.

In this case, the evaporation crucible can always occupy a fixed position. However, relative movement may be realized by circularly moving the evaporation crucible through the bracket 44, for example. The connection between the evaporation crucible and point 0 is the center normal
32 together with the deposition angle θ °. As long as the deposition crucible remains on line 52, the deposition angle θ ° is relevant even if the deposition angle for all remaining points on the support member changes. A suitable deposition angle θ ° is, for example, about 45 °, but this also depends on other deposition parameters such as the temperature of the support member, the rotation speed and the deposition speed.

A preferred value for the temperature of the support member is to start at about room temperature and adapt the deposition rate to a predetermined heat flow from the support member so that the screen temperature does not exceed about 200 ° C. If desired, the deposition can be performed sequentially from a plurality of crucibles. For example, the height of the deposition crucible measured from a plane 54 perpendicular to the axis 32 through the center point 50 determines the deposition angle outside the center of the support member, as well as the local distance between the support member and the deposition crucible. Also, in this way, a change in the thickness of the light-emitting layer on the screen can be affected together with the constant deposition angle. From another point of view, the optimum position of the evaporation crucible with respect to the screen can be determined in this way, and if the optimum position is highlighted, the support member can be further tilted with respect to the evaporation crucible during the evaporation.
In this way, for example, the distance between the deposition angle and the screen edges A and B can always be equal to each other. In that case, the deposition angle θ ° will vary, but the nominal value for the optimal angle of incidence is not so strict if large enough, so that some variation may be tolerable and even preferred. I knew it wasn't. In fact, it is not excluded that changes in the deposition angle during deposition also at least partially contribute to the optimization of the structure in the light-emitting layer. This assumption is based on the fact that, despite the relatively large differences in deposition angles measured in the screen, a luminescent layer with a satisfactory uniform structure is obtained (as long as it is important). Supported by

As is evident from the above, it is clear that various parameters affect the structure of the light emitting layer, and that the technical margin is also a factor in the deposition. Since the value of the deposition angle is not critical if sufficiently large, always find a satisfactory compromise between the different requirements for the layer thickness and its variation over the screen and the different geometrical configurations of the support members. Can be. An additional advantage of the adaptation technique according to the invention is that the entire layer can be applied in a single operation, so that small interruptions in the thickness direction are also prevented. If the deposition angle is relatively small, the structure of the screen will be very close to that of known screens, whereas if the deposition angle is relatively large, the columns of CsI will be placed far apart from each other and For example, the filling factor of the screen, and hence the X-ray absorption, is reduced. Furthermore, in the case of vapor deposition at a larger angle, it will be much less practical, such as inefficient use of CsI.

In special cases, for example, especially where very high resolution is required, structures comprising substantially separate columns can be used. In that case, optical crosstalk is completely prevented. The gap can in principle be filled with an X-ray absorbing non-emissive material.

In the case of geometries where it is not possible to obtain an acceptable compromise for relative positioning etc.
For example, a solution can be found by flame spraying or plasma spraying the luminescent material. The support member is effectively scanned with a relatively small nozzle (relative movement of both), while the distance from the support member is freely selected within wide limits and, for example, by tilting the nozzle any desired The angle can be adjusted locally. In addition, procedures can be taken in which most of the luminescent material is used effectively. In the case of flame spraying or plasma spraying,
The remaining requirements, such as the temperature of the support member, the rate of deposition, the nature of the material being deposited, etc., must be such that they do not deviate too much from the values used during the deposition, because otherwise the desired This is because a layer having the ore column structure cannot be obtained.

For comparison, FIG. 3 shows photographs taken by a scanning electron microscope of a layer having a known structure and a test layer according to the present invention. These are all plan views, that is, photographs taken from a direction away from the support member. The known layer shown in FIG. 3a clearly shows relatively wide cracks (cracks) 60 (see especially FIG. 3a1)), and therefore also shows relatively large cavities 62, as is evident from FIG. 3a3). The layers made according to the invention shown in FIG. 3b have very small width cracks 64, as can be seen from FIG.
As is clear from 3), it has a relatively small cavity 66. By optimizing the overall adaptation technique, for example, cracks having a width clearly greater than 0.5-1 μm can be completely prevented. Figures 3b1) and 3b2) clearly show a very regular structure and a relatively large filling factor due to the absence of wide gaps or cavities occurring in the known layers. Due to the improved structure,
If desired, the layers according to the invention can be even thicker, for example 400-500 μm, without loss of resolution. The regular structure allows a more continuous photocathode to be disposed on the layer with or without the addition of an intermediate layer. As a result, parts of this layer can also be optimized without a rough structure with wide gaps or cavities, thus leading to severe restrictions.

[Brief description of the drawings]

FIG. 1 shows an X-ray image intensifier according to the present invention.

FIG. 2 shows diagrammatically an apparatus for implementing the method according to the invention.

FIG. 3a shows the grain structure at three different magnifications in the plane of the conventional light-emitting layer, and FIG. 3b shows the grain structure at three different magnifications in the plane of the light-emitting layer according to the invention.

[Explanation of symbols]

 1: X-ray image intensifier tube 8: Inlet screen 20, 34: Support member 22: Light emitting material layer 21: Photocathode 32: Axis 36: Evaporating crucible 38: Heating element 0: Center point θ °: Evaporation angle

Continuation of the front page (71) Applicant 590000248 Groenewoodseweg 1, 5621 BA Eindhoven, The Netherlands (72) Inventor Offnot Leonard Hermann Simon's Netherlands Heerlen Jääm Camperstraatstraat 5

Claims (6)

[Claims] 1. A method of manufacturing an X-ray image intensifier having an entrance screen having a support member on which a light-emitting material layer and a photocathode are disposed, wherein the light-emitting material layer is oblique to a center line perpendicular to the screen. A method for manufacturing an X-ray image intensifier tube, comprising: depositing by vapor deposition; and raising the temperature of the support member from room temperature to a maximum temperature during the deposition of the light emitting material layer. 2. The method according to claim 1, wherein the maximum temperature is less than 200 ° C. 3. The method according to claim 1, wherein the luminescent material layer is deposited by vapor deposition at an angle of about 40 ° to 50 ° with respect to a center line perpendicular to the screen. 13. The method for producing an X-ray image intensifier tube according to the above item. 4. The method according to claim 1, wherein the step of depositing the light-emitting material layer comprises rotating the support member about a center line perpendicular to the support member with respect to the light-emitting material source. Item 4. The method for producing an X-ray image intensifier tube according to item 2, item 2 or item 3. 5. The light-emitting material source according to claim 1, wherein the light-emitting material source makes a circular motion around a center line perpendicular to the support member. A method for manufacturing an X-ray image intensifier tube. 6. The light-emitting material layer according to claim 1, wherein the support member performs a tilting movement with respect to the light-emitting material source during the step of applying the light-emitting material layer. A method for producing the X-ray image intensifier tube according to claim 1.